In recent years, there has been a growing interest in electrical installations on the seabed. In bringing power electronics subsea, two general concepts exist: (1) the equipment stays at atmospheric pressure; and (2) the equipment is pressurized to the hydrostatic pressure level on seabed.
Concept (1) has the advantage that standard electric/electronic components, known from onshore installations, can be used, while disadvantages include thick walls needed for the enclosure to withstand the pressure difference between inside and outside. Thick walls make the equipment heavy and costly and in addition prevent efficient cooling of the internal electric/electronic components. Also, the pressure difference sets high requirements on seals and penetrators.
Concept (2) has the advantage that no thick walls are needed for the enclosure since no or only a relatively small pressure difference exists between inside and outside. Disadvantages are that the electric/electronic components must be able to cope with the prevailing pressure, and that reliable pressure compensation must be provided for.
In electrical power transmission and distribution, a circuit breaker can be defined as a fault triggered electrical switch with the purpose of protecting electrical consumers and cables from abnormal situations such as short circuit or overload. The switch comprises two contacts which are brought to engagement or disengagement by an actuator. The actuator is typically electro-mechanical. A control means is arranged to detect abnormal situations, or faults, and in response thereto send a signal to the actuator which then separates the contacts whereby power is cut off.
In addition to being fault triggered, a circuit breaker can usually also be command controlled. The above mentioned control means then receives a command from an operator or from a control system and in response thereto sends a signal to the actuator which opens or closes the switch.
Traditionally when circuit breakers are used in subsea power distribution systems, a circuit breaker is placed inside a closed enclosure together with its electro-mechanical actuator. GB2463487 A discloses a subsea electrical protection device which comprises a re-settable circuit breaker. U.S. Pat. No. 6,762,662 B2 discloses a hermetically sealed electrical switch comprising magnetic force transfer means. The hermetically sealed electrical switch of U.S. Pat. No. 6,762,662 B2 is however not suitable for subsea use, especially not for “deepwater subsea” due to the prevailing pressure at great depths, at least 1000 m.